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.\" $OpenBSD: semget.2,v 1.5 1998/07/20 07:37:24 deraadt Exp $
.\" $NetBSD: semget.2,v 1.2 1997/03/27 08:20:41 mikel Exp $
.\"
.\" Copyright (c) 1995 Frank van der Linden
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed for the NetBSD Project
.\" by Frank van der Linden
.\" 4. The name of the author may not be used to endorse or promote products
.\" derived from this software without specific prior written permission
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"/
.Dd August 17, 1995
.Dt SEMGET 2
.Os
.Sh NAME
.Nm semget
.Nd get semaphore set
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/ipc.h>
.Fd #include <sys/sem.h>
.Ft int
.Fn semget "key_t key" "int nsems" "int semflg"
.Sh DESCRIPTION
The
.Fn semget
system call returns the semaphore identifier associated with
.Fa key .
A new set containing
.Fa nsems
semaphores is created if either
.Fa key
is equal to IPC_PRIVATE, or
.Fa key
does not have a semaphore set associated with it and the IPC_CREAT bit is
set in
.Fa semflg.
The access modes of the created semaphores is specified in
.Fa semflg
by
.Em or Ns 'ing
the following values
.Pp
.Bd -literal -offset indent -compact
SEM_A alter permission for owner
SEM_R read permission for owner
SEM_A >> 3 alter permission for group
SEM_R >> 3 read permission for group
SEM_A >> 6 alter permission for other
SEM_R >> 6 read permission for other
.Ed
.Pp
If a new set of semaphores is created, the data structure associated with it
(the
.Va semid_ds
structure, see
.Xr semctl 2 )
is intialized as follows:
.Bl -bullet
.It
.Va sem_perm.cuid
and
.Va sem_perm.uid
are set to the effective uid of the calling process.
.It
.Va sem_perm.gid
and
.Va sem_perm.cgid
are set to the effective gid of the calling process.
.It
.Va sem_perm.mode
is set to the lower 9 bits of
.Fa semflg .
.It
.Va sem_nsems
is set to the value of
.Fa nsems
.It
.Va sem_ctime
is set to the current time
.It
.Va sem_otime
is set to 0
.El
.Sh RETURN VALUES
.Fn semget
returns a non-negative semaphore identifier if successful. Otherwise, -1
is returned and
.Va errno
is set to reflect the error.
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EACCES
The caller has no permission to access a semaphore set already associated with
.Fa key.
.It Bq Er EEXIST
Both IPC_CREAT and IPC_EXCL are set in
.Fa semflg ,
and a semaphore set is already associated with
.Fa key .
.It Bq Er EINVAL
.Va nsems
is less than 0 or greater than the system limit for the number in a semaphore
set.
A semaphore set associated with
.Fa key
exists, but has fewer semaphores than the number specified in
.Fa nsems .
.It Bq Er ENOSPC
A new set of semaphores could not be created because the system limit
for the number of semaphores or the number of semaphore sets has been
reached.
.It Bq Er ENOENT
IPC_CREAT was not set in
.Fa semflg
and no semaphore set associated with
.Fa key
was found.
.El
.Sh SEE ALSO
.Xr semctl 2 ,
.Xr semop 2
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